1. Field of the Invention
The present invention relates to a polyethylene terephthalate resin molded product good in appearance, surface gloss, mechanical characteristics and light fastness, a polyethylene terephthalate resin composition enabling the production of said molded product, and a method for modifying a polyethylene terephthalate resin.
2. Description of the Prior Art
Being good in mechanical properties, gas-blocking property, chemical resistance, flavor-retaining property, transparency, hygienic property, etc., polyethylene terephthalate resins are widely used after processing into various parts, fibers, sheets, tubes, containers, etc.
For some applications, it is necessary to provide additional functions for polyethylene terephthalate resins by coloring. Polyethylene terephthalate resins are colored for light shading, decoration, color identification, improvement of light fastness of plastics, content protection or masking, and for other purposes; black colored molded products are industrially most common and important.
Traditionally, black coloring of polyethylene terephthalate resins has been achieved using black pigments represented by carbon black. For example, there have been various attempts to impart a black color to polyethylene terephthalate resins, including the multiple color dope dyed polyethylene terephthalate film described in Japanese Patent Unexamined Publication No. 40347/1974, prepared by mixing a polyethylene terephthalate resin containing carbon black added at the time of polymerization, with other pigments; the production method for dope dyed polyester pellets described in Japanese Patent Unexamined Publication No. 250034/1986, wherein dope dyed polyester pellets prepared by mixing polyethylene terephthalate with a pigment (e.g., carbon black) are produced after a masterbatch is prepared by mixing the polyester and the pigment in a molten state; the polyethylene terephthalate resin composition described in Japanese Patent Unexamined Publication No. 281070/1990, prepared by adding a spherical iron oxide of the hematite structure to a polyethylene terephthalate resin; and the black polyester coloring agent described in Japanese Patent Unexamined Publication No. 194825/1993, wherein carbon black is dispersed in a mixed resin of a polyethylene terephthalate resin and a polybutylene terephthalate resin.
Also, fiber-reinforced polyethylene terephthalate resins are used in electronic parts, automobile parts, electric appliance parts, etc., since they possess as excellent physical properties (mechanical strength, modulus of elasticity, impact strength, thermal deformation resistance, etc.) for molding materials as those of thermosetting resins.
Previous attempts to color fiber-reinforced polyethylene terephthalate resins include the polyester resin composition for molding described in Japanese Patent Unexamined Publication No. 117951/1990, comprising a polyethylene terephthalate having a specific viscosity of not less than 0.35, a reinforcing material, and carbon black; the composition for molding described in Japanese Patent Unexamined Publication No. 261462/1992, comprising a polyethylene terephthalate and glass fiber, as well as an aliphatic polyester, a metal salt of an ionic hydrocarbon copolymer, an antioxidant, a secondary amide, and carbon black as a coloring agent; and the polyethylene terephthalate resin composition reinforced with antistatic glass fiber described in Japanese Patent Unexamined Publication No. 53610/1996, comprising a glass-fiber-reinforced polyethylene terephthalate resin having a volume resistivity of not more than 1.times.10.sup.10 .OMEGA..multidot.cm and carbon black.
In recent years, there has been strong commercial demand for a polyethylene terephthalate resin composition possessing improved light fastness, since polyethylene terephthalate resin products have been widely used outdoors. Also, there has been strong demand for molded products of high precision in details for use in electrical appliance parts and automobile product parts.
When a polyethylene terephthalate resin is colored black using a black pigment (e.g., carbon black, phthalocyanine black), as in the prior art, the black pigment is not readily finely dispersed in the resin, even after long kneading, resulting in decreased physical properties and light fastness, in comparison with natural resins that do not contain a coloring agent. Also, when a glass-fiber-reinforced polyethylene terephthalate resin is colored black using a black pigment, fluidity of the glass-fiber-reinforced resin and surface gloss of the molded product are considerably reduced, and in some cases warp deformation due to thermal change increases during the molding process.
In view of the above problems in the prior art, the object of the present invention is to provide a polyethylene terephthalate resin molded product that is uniformly colored black and that is good in surface gloss, light fastness, mechanical characteristics and thermal dimensional stability, and a polyethylene terephthalate resin composition enabling the production of said molded product.